It is a long range goal of this project to discover how SV40 causes transformation. SV40 is a small DNA virus of the papova virus group. Papovaviruses have been implicated in cancer and progressive multifocal leukoencephalopathy. Current topics of interest are (1) the cell cycle in normal and SV40 transformed cells, (2) the origin and structure of the tumor specific transplantation antigen, (3) the structure of SV40 chromatin, (4) regulation of the synthesis of SV40 tumor antigen, (5) the structure and function of the tumor antigen, and (6) the mode of DNA replication in normal and transformed cells.